The invention relates to improvements in fittings of the type disclosed in commonly owned U.S. Pat. No. 5,048,872, granted Sep. 17, 1991, for "Fitting for cables, tubes and the like". The disclosure of this patent is incorporated herein by reference.
Fittings of the type to which the present invention pertains include an externally threaded first component (e.g., a sleeve), an internally threaded second component (e.g., a nut) which can be moved into mesh with the first component, and a set of prongs which can be flexed to engage the outer surface of a rod, cable, tube, hose or other object or article extending through aligned coaxial passages of the two components. The flexing is effected by an annular deforming surface which is provided in one of the components and engages the end faces of the prongs in response to threading of the first component into the second component.
Conventional fittings of the above outlined character are furnished in several sizes, and each size is designed to be used with articles or objects having outer diameters within a particular range. Thus, a first fitting will be used to sealingly and/or clampingly engage the outer surfaces of articles having a diameter within a relatively narrow first range, a second fitting will be used to sealingly and/or clampingly engage the outer surfaces of articles having a diameter within a relatively narrow second range, and so forth. In many instances, the externally and/or internally threaded components of such fittings are made of a plastic material which can create problems if the connection between the fitting and a rod-shaped or tubular article is to withstand pronounced tensional stresses. The situation is aggravated if the connection is also called upon to establish a fluidtight seal at the locus of engagement of flexed prongs with the outer surface of a rod-shaped or tubular object or article.
The rules and regulations by authorities in many countries also create problems in connection with the making and using of fittings of the above outlined character. For example, the authorities in charge of regulating the utilization of such fittings in certain countries prescribe identical norms for all sizes of fittings. Thus, the prescribed tensional stress to be withstood by a fitting which is designed to engage articles of small or very small diameter is the same as that to be withstood by much larger fittings which are designed to clampingly engage and/or establish sealing connections with articles having a large or very large diameter. In actual practice, a fitting which is designed to clampingly and/or sealingly engage an article having a relatively small diameter cannot withstand the stresses which are expected to be withstood by a fitting for use with articles having larger or very large diameters. In other words, whereas certain sizes of fittings meet the prescribed norms, the remaining sizes cannot be put to use because the regulations cannot be met when the fitting is designed to engage a workpiece having a small or very small outer diameter. Additional problems arise because the authorities in many countries prescribe the materials which can be used to make the parts of the fittings. This greatly reduces the selection of materials which can be used to make fittings capable of satisfying the aforediscussed strict requirements.
Many authorities also prescribe the dimensions and the nature of internal and external threads on the components of fittings for use in connection with cables or the like, and the authorities even prescribe the dimensions and the shape of normally polygonal portions of nuts and sleeves which are provided to facilitate engagement by a wrench, by pliers or by any other suitable tool which must be used to hold the respective component against rotation and/or to rotate the particular component relative to the other component or components. Still further, the authorities in certain countries even prescribe the range of outer diameters of workpieces which can be used in conjunction with fittings of a particular size. In other words, the regulations in many countries are of such nature that the manufacturer is free to select only the size and/or the shape of the flexible prongs, of the deforming surface or surfaces and possibly the size and/or shape of discrete seals which are to be used in order to establish a sealing connection between the fitting and the rod-shaped or tubular article which is to be sealingly and/or clampingly engaged by the fitting. Even these parameters cannot be selected at will because the maker of the fittings is required to avoid designs which would necessitate the application of large forces in order to drive the externally threaded component into the internally threaded component and to thereby flex the prongs toward sealing and/or clamping engagement with the outer surface of a rod-shaped or tubular article which extends through the aligned axial passages of such components. Still further, the manufacturer must take into consideration the requirement to maintain the overall length of the partly assembled or fully assembled fitting within a desired range. The inclination of the deforming surface which is caused to flex the prongs in response to penetration of the externally threaded component into the internally threaded component of the fitting determines the torque which must be applied to assemble the fitting with an article as well as the overall length of the fully assembled fitting.
German Utility Model No. G 84 15 525.6 of Holzmann (published Oct. 11, 1984) discloses a threaded fitting which can be used with cables and is characteristic of numerous presently available fittings serving to clampingly and/or sealingly engage the outer surface of a cable or the like. The dimensions (particularly the radial dimensions) of the prongs in the fitting of Holzmann are selected in such a way that they provide room for insertion of a relatively thick cylindrical seal. The seal is deformed into fluidtight engagement with the outer surface of an article to be clamped in response to radially inward flexing of the prongs. This is achieved by reducing the thickness of the prongs accordingly, i.e., the prongs are rather thin as measured in a direction radially of the tubular component which carries the prongs. The thin prongs provide adequate clearance for insertion of a relatively thick cylindrical seal which is biased against the outer surface of an article when the fitting of Holzmann is assembled. The fitting of Holzmann further exhibits the feature (which, at a first glance, could be interpreted as an advantage) that a relatively small torque suffices to engage the fitting with a cable or the like because the relatively thin and readily flexible prongs as well as the rather thick elastic seal can be readily deformed in response to penetration of the externally threaded component into the internally threaded component. Of course, such fittings cannot offer a pronounced resistance to a pull, i.e., to axial movement of the fitting relative to a cable and/or vice versa.
Holzmann proposes to further weaken the relatively thin and readily flexible prongs by the provision of a recess in that end portion of each prong which is of one piece with the adjacent axial end of the externally threaded component. Such recess is provided in the external surfaces of the prongs and its depth approximates half the thickness of a prong. The recess ensures that each prong is flexed at a point adjacent the closed ends of axially parallel slots which alternate with the prongs. Initial flexing of the prongs about pivot axes at the external recess can be effected in response to the exertion of a relatively small force (torque). However, such force must be increased rather abruptly when the prongs are thereupon bent intermediate their ends in response to further penetration of the externally threaded component into the internally threaded component. In fact, the torque which must be applied to deform the prongs between their ends is just as large as that which is required to flex prongs having no recesses of the type proposed by Holzmann.
Proposals to influence the function of fittings include the provision of prongs having a particular size and shape in order to enhance the clamping force between the prongs and a cable or the like as well as to enhance the ability of the assembled fitting to resist tensional stresses. The proposals have met with some success in connection with the making of relatively large fittings for engagement with articles having a large outer diameter but they have failed when a fitting is to be brought into clamping and sealing engagement with articles (e.g., cables) having a relatively small outer diameter. For example, it was proposed to employ relatively long prongs in order to ensure the establishment of large-area contact between a deformed prong and the outer surface of an article or between a deformed prong and a tubular seal which is to be inserted between the prongs and the outer surface of the article. The relatively long prongs are likely to project from the passage of the internally threaded component before the threading of the externally threaded component into the internally threaded component is completed. This does not entail any further increase of the clamping and/or sealing action. Since the prongs are relatively thin, those portions of such prongs which extend outwardly beyond the internally threaded component of the fitting are likely to be bent radially outwardly by an article which is elastically or resiliently deformable and has stored energy during application of the fitting. Such outward flexing weakens the sealing and/or clamping action and hence the resistance of the applied fitting to stand pronounced tensional stresses in a direction to move it axially of the article. The reason is that only those portions of the deformed prongs which do not project beyond the internally threaded component offer resistance to tensional and/or other stresses which develop when the fitting is applied in order to clampingly and/or sealingly engage a cable or the like.
Relatively thick cylindrical seals also exhibit a number of drawbacks. The main drawback is that the thickness of the seal can be increased only by reducing the thickness of the prongs; this creates the aforediscussed problems. The reason for the utilization of rather thick cylindrical seals is that they are less likely to undergo unpredictable deformation during flexing of the prongs against the external surface of a seal. However, a relatively thick seal must undergo very pronounced radial deformation before it can establish a reliable sealing and frictional engagement with the outer surface of a rod-shaped or tubular article. If the seal is not subjected to pronounced deformation, it merely acts as a cushion and can readily slide along the outer surface of a cable or the like. The forces which must be applied in order to adequately constrict a relatively thick cylindrical seal are often so large that the densification of the material of the constricted seal results in the generation of a radially outwardly directed reaction force which must be taken up by the externally threaded component of the fitting. Such problem is likely to arise when the fitting is relatively small and is to be applied to an article having a small or very small outer diameter. It has been found that the reaction force is likely to cause bursting or cracking of the threaded components, especially in the region of their threads. Moreover, further rotation of the mating components cannot result in additional stressing of the seal, i.e., such rotation does not result in further penetration of the externally threaded component into the internally threaded component because the two threads are out of mesh. Attempts to overcome such problems involve the formation of specifically designed threads having deeper grooves; this even further reduces the ability of the corresponding components to withstand the aforediscussed reaction forces.
All in all, heretofore known fittings are incapable of satisfying the requirements which are prescribed by authorities and/or the requirements by users of the fittings. Such requirements include shortness of the fully assembled fitting, elimination of the danger of destruction under the influence of reaction forces, assembly with a cable or the like in response to the application of a relatively small force, and the ability of a fitting to be connectable with articles having relatively small or relatively large outer diameters.